GM Service Manual Online
For 1990-2009 cars only
3X Crank Sensor: Indicates engine RPM based on the 3X reference signal input to the powertrain control module (PCM).

18X Crank Sensor: Indicates engine RPM based on the 18X reference signal input to the PCM.

1-2 Solenoid Circuit Status: Indicates the diagnostic state of the 1-2 solenoid control circuit. The scan tool displays Fault, OK, or Invalid State.

2-3 Solenoid Circuit Status: Indicates the diagnostic state of the 2-3 solenoid control circuit. The scan tool displays Fault, OK, or Invalid State.

A/C High Side Pressure Sensor: The scan tool displays 0-5 volts. Represents the A/C refrigerant pressure sensor signal. The amount of pressure indicates the amount of load that the A/C compressor is placing on the engine. The PCM uses this information in order to adjust idle and in order to control the cooling fans.

A/C Off For WOT: The scan tool displays YES or NO. Indicates whether A/C is commanded OFF due to wide open throttle (WOT).

A/C Pressure Disable: The scan tool displays YES or NO. Indicates whether A/C is commanded OFF due to excessive or insufficient pressure.

A/C Relay Circuit Status: The scan tool displays OK, Fault, or Invalid State. Indicates the diagnostic state of the A/C relay control circuit.

A/C Relay Command: The scan tool displays ON or Off. Indicates intended PCM output to the A/C relay.

A/C Request Signal: The scan tool displays YES or NO. Indicates if A/C operation has been requested.

Air Fuel Ratio: The scan tool range is 0.0-25.5. Air fuel ratio indicates the PCM commanded value. In Closed Loop, air fuel ratio should normally be around 14.2-14.7. A lower air fuel ratio indicates a richer commanded mixture, which may be seen during power enrichment or three-way catalytic converter (TWC) protection modes. A higher air fuel ratio indicates a leaner commanded mixture. This can be seen during decel fuel Mode.

BARO: The scan tool range is 10-105 kPa/0-5 volts. The barometric pressure (BARO) reading is determined from the manifold absolute pressure (MAP) sensor signal monitored during key up and wide open throttle (WOT) conditions. BARO is used to adjust fuel delivery and spark advance to compensate for altitude changes.

Boost Solenoid Circuit Status (L67): Indicates the diagnostic state of the output driver for the boost solenoid control circuit. The scan tool displays Fault, OK or Invalid State

Boost Solenoid Command (L67): Indicates the commanded state of the boost solenoid. The scan tool displays percent.

CMP Sensor Signal Present: Indicates if the PCM is receiving the cam sensor reference signal from the ignition control module (ICM). The scan tool displays YES or NO.

Cruise Control Active:  The scan tool displays ENGAGED or DISENGAGED. Represents the state of the Cruise Status Input from the SMCC module. Cruise should not display ENGAGED unless the vehicle is operating in cruise control.

Cruise Inhibit Reason: The scan tool displays VEHICLE SPEED, BRAKE, or CLUTCH. Indicates the reason cruise is being inhibited.

Cruise Inhibit Signal Circuit Status: Indicates the diagnostic state of the output driver for the cruise inhibit signal circuit. The scan tool displays Fault, OK or Invalid State.

Cruise Inhibit Signal Command: Indicates if cruise is being inhibited. The scan tool displays YES or NO.

Current Gear: The scan tool displays numbers 1, 2, 3, or 4. The PCM looks at trans range position and the gear commanded by the PCM. The actual forward gear that the transaxle is in will be the lower of the two because the manual valve can override the PCM commanded gear.

Cycles of Misfire Data: The scan tool range is 0-99 counts. Indicates the total number of cylinder firing events that were detected as being misfires during the last 200 crankshaft revolution sample period.

Cyl. 1-6 Injector Circuit History: The scan tool displays Fault or OK This parameter saves the state of the driver circuit for this device.

Cyl. 1-6 Injector Circuit Status: The scan tool displays Fault or OK This parameter indicates the state of the driver circuit for this device.

Decel Fuel Cutoff: The scan tool displays ACTIVE or INACTIVE. ACTIVE displayed indicates that the PCM has detected conditions appropriate to operate in deceleration fuel mode. The PCM will command deceleration fuel mode when a sudden decrease in throttle position has been detected while the vehicle is traveling over 40 km/h (25 mph). While in deceleration fuel mode, the PCM will decrease the amount of fuel delivered by entering Open Loop and decreasing the injector pulse width.

Desired EGR Position: The scan tool displays volts or a range from 0-100 percent. Represents the exhaust gas recirculation (EGR) pintle position that the PCM is commanding. Desired EGR position should stay close to EGR position sensor.

Desired Idle Speed: The scan tool range is 0-3187 RPM. Represents the idle speed that is commanded by the PCM. The PCM will compensate for various engine loads based on engine coolant temperature (ECT) to keep the engine at the desired idle speed.

Driver Module 1 Status: Indicates the diagnostic state of the module. The scan tool displays Enabled, Off-High Volts, Off-High Temp, or Invalid State.

Driver Module 2 Status: Indicates the diagnostic state of the module. The scan tool displays Enabled, Off-High Volts, Off-High Temp, or Invalid State.

Driver Module 3 Status: Indicates the diagnostic state of the module. The scan tool displays Enabled, Off-High Volts, Off-High Temp, or Invalid State.

Driver Module 4 Status: Indicates the diagnostic state of the module. The scan tool displays Enabled, Off-High Volts, Off-High Temp, or Invalid State.

ECT Sensor: The scan tool range is -40 to +151°C (-40 to +304°F). The engine coolant temperature (ECT) sensor is mounted in the coolant stream. The PCM applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold, internal resistance high, the PCM monitors a high signal voltage and interprets the higher voltage as a cold engine. As the sensor warms, internal resistance decreases, the voltage signal decreases and the PCM interprets the lower voltage as a warm engine.

EGR Flow Test Count: The scan tool range is 0-255. Indicates the number of EGR flow test samples collected during the current ignition cycle. The maximum number of samples allowed is 1 during normal operation. If the PCM battery feed has been disconnected or a DTC P0401 has been cleared, several EGR flow test samples will be allowed during the next ignition cycle. This allows repair verification during a single ignition cycle.

EGR Learned Minimum Position: The scan tool range is 0-5 volts. Represents the learned voltage that the PCM uses to determine whether or not the EGR valve is fully closed, 0 percent pintle position. If the Desired EGR Position is 0 percent and a difference of more than 0.4 volt between EGR Feedback and EGR Closed Valve Pintle Position is detected, DTC P1404 will set.

EGR Position Sensor: The scan tool range is 0-5 volts. Indicates the EGR pintle position sensor signal voltage being monitored by the PCM. A low voltage indicates a fully extended pintle, closed valve, a voltage near 5 volts indicates a fully retracted pintle, open valve.

EGR Position Sensor: The scan tool range is 0-100 percent. Represents the actual position of the EGR pintle in percent. 0 percent displayed indicates a fully extended pintle, EGR valve closed.

EGR Position Variance: The scan tool range is 0-100 percent. Indicates the difference between desired EGR position and actual EGR position currently being monitored by the PCM. If the EGR position variance reaches an unacceptable level, DTC P1404 will set.

EGR Solenoid Circuit History: The scan tool displays Fault or OK This parameter saves the state of the driver circuit for this device.

EGR Solenoid Circuit Status: Indicates the diagnostic state of the output driver for the EGR solenoid circuit. The scan tool displays Fault, OK or Invalid State.

EGR Solenoid Command: The scan tool range is 0-100 percent. Represents the EGR valve driver pulse width modulation (PWM) signal from the PCM. A duty cycle of 0 percent indicates that no EGR flow is being commanded. A 100 percent duty cycle indicates maximum EGR flow commanded.

Engine Load: The scan tool range is 0-100 percent. Engine load is calculated by the PCM from engine speed and mass air flow (MAF) sensor readings. Engine load should increase with an increase in RPM or air flow.

Engine Oil Life Remaining: The scan tool range is 0-100 percent. Indicates the engine oil life index. The PCM calculates engine oil life based upon the number of engine revolutions seen and operating conditions such as calculated oil temperature. Pressing the oil life monitor reset switch will return the displayed engine oil life to 100 percent.

Engine Oil Pressure Sensor: The scan tool range is 0-5 volts. Represents the engine oil pressure sensor signal voltage. The PCM transmits engine oil pressure information to the IPC via class 2 serial data. The normal range of the engine oil pressure sensor is between 0.5 volt at 0 kPa (0 psi) and 4.5 volts at 883 kPa (128 psi).

Engine Run Time: The scan tool range is 00:00:00-99:99:99 Hrs:Min:Sec. Indicates the time elapsed since the engine was started. If the engine is stopped, ENGINE RUN TIME will be reset to 00:00:00.

Engine Speed: The scan tool range is 0-9999 RPM. Engine speed is computed by the PCM from the 3X reference input. The engine speed should remain close to desired idle under various engine loads with engine idling

EVAP Fault History: The scan tool displays No Fault, Excess Vacuum, Purge Valve Leak, Small Leak, or Weak Vacuum.

EVAP Purge Solenoid Circuit Status: Indicates the diagnostic state of the output driver for the evaporative emission (EVAP) purge solenoid circuit. The scan tool displays Fault, OK or Invalid State.

EVAP Purge Solenoid Command: The scan tool range is 0-100 percent. Represents the PCM commanded pulse width modulated (PWM) duty cycle of the EVAP purge valve. 0 percent displayed indicates no purge. 100 percent displayed indicates full purge.

EVAP Vent Solenoid Circuit Status: Indicates the diagnostic state of the output driver for the EVAP vent solenoid circuit. The scan tool displays Fault, OK or Invalid State.

EVAP Vent Solenoid Command: The scan tool range is 0-100 percent. Represents the PCM commanded PWM duty cycle of the EVAP vent valve. 0 percent displayed indicates no purge. 100 percent displayed indicates full purge.

Extended Travel Brake Switch: Indicates the state of the extended travel brake switch. The scan tool displays Applied or Released.

FC Relay 1 Circuit Status: Indicates the diagnostic state of the output driver for the FC Relay 1 Circuit. The scan tool displays Fault, OK or Invalid State.

FC Relay 1 Command: Indicates the commanded state of the FC Relay 1. The scan tool displays ON or OFF.

FC Relay 2 and 3 Circuit Status: Indicates the diagnostic state of the output driver for the FC Relay 2 and 3 Circuit. The scan tool displays Fault, OK or Invalid State.

FC Relay 2 and 3 Command: Indicates the commanded state of the FC Relay 2 and 3. The scan tool displays ON or OFF.

Fuel Pump Relay Circuit History Status: The scan tool displays Fault or OK This parameter displays the state of the driver circuit for this device.

Fuel Pump Relay Circuit Status: Indicates the diagnostic state of the output driver for the fuel pump relay control circuit. The scan tool displays Fault, OK or Invalid State.

Fuel Pump Relay Command: The scan tool displays ON or OFF. Indicates the PCM commanded state of the fuel pump relay control circuit.

Fuel Tank Level Remaining: Indicates the level of fuel remaining in the fuel tank. The scan tool displays percent.

Fuel Tank Pressure Sensor: The scan tool displays 0-5 volts or -17.5 to +7.5 in of H2O Fuel tank pressure is used extensively for EVAP purge control and EVAP system diagnostics.

Fuel Trim Cell: The scan tool range is 0-9. Fuel trim cell is dependent upon engine speed and mass air flow (MAF) sensor readings. A plot of RPM vs. MAF is divided into 10 cells. Fuel trim cell indicates which cell is currently active.

Fuel Trim Learn: The scan tool displays NO or YES. When conditions are appropriate for enabling long term FT corrections, FUEL TRIM LEARN will display yes. This indicates that the long term FT is responding to short term fuel trim. If the fuel trim Learn displays NO, long term FT will not respond to changes in short term FT.

Gen F-Terminal Signal: The scan tool range is 0-100 percent. Represents the field terminal input from the generator. The field PWM duty cycle indicates generator output level. A higher duty cycle indicates a higher generator output. The PCM uses the generator F terminal signal in order to adjust spark and idle air control (IAC) to compensate for variances in engine load caused by the generator.

Gen L-Terminal Command: The scan tool displays ON or OFF. OFF displayed indicates that the PCM has commanded the generator control circuit OFF.

HO2S 1:  The scan tool range is 0-1,132 mV. Represents the fuel control exhaust oxygen sensor output voltage. Should fluctuate constantly within a range between 10 mV, lean exhaust, and 1,000 mV, rich exhaust, while operating in Closed Loop.

HO2S 2: The scan tool range is 0-1,132 mV. Represents the catalyst monitor exhaust oxygen sensor output voltage. If the catalyst is operating efficiently, the heated oxygen sensor (HO2S) 1 signal will be far more active than that produced by the HO2S 2 sensor. If the PCM detects a level of HO2S 2 activity that indicates the catalyst is no longer operating efficiently, DTC P0420 will be set.

IAC Position: The range is 0-255. This displays the commanded position of the idle air control pintle in counts. A larger number of counts means that more air is being commanded through the idle air passage. IAC position should respond fairly quickly to changes in engine load to maintain desired idle RPM.

IAT Sensor: The scan tool range is -40 to +151°C (-40 to +304°F). The PCM converts the resistance of the IAT sensor to degrees. The PCM uses intake air temperature (IAT) in order to adjust fuel delivery and spark timing according to incoming air density. IAT is also compared to engine coolant temperature (ECT) at startup to identify cold starts for the HO2S heater and the EVAP diagnostics.

Ignition 1 Signal: The scan tool range is 0-25.5 volts. Represents the system voltage measured by the PCM at the PCM ignition feed.

Ignition Mode: The scan tool displays BYPASS or IC. Indicates the commanded state of the Bypass signal output from the PCM. When BYPASS is displayed, the ignition control module (ICM) is controlling the spark advance at a fixed 10 degrees before top dead center (BTDC), bypass mode. IC displayed indicates that the PCM has requested control of the spark advance, IC mode. The ignition control module determines the correct operating mode based on the level of voltage that the PCM applies to the ignition control module bypass circuit. The PCM provides 5 volts to the ignition control module bypass circuit when conditions are appropriate for PCM control of spark timing (IC mode). If the PCM does not apply 5 volts to the bypass circuit, or if the ignition control module does not receive the voltage, the module will control spark timing.

IMS: This parameter displays the state of the transmission internal made switch based on the signal from the IMS inside the transmission. The scan tool will display Drive 1, Drive 2, Drive 3, Drive 4, Reverse, or Neutral. Drive 1 indicates the transmission range switches C and P are closed, connecting these circuits to ground. Drive 2 indicates the transmission range switches A and C are closed, connecting these circuits to ground. Drive 3 indicates that all of the transmission range switches are closed, connecting all four circuits to ground. Drive 4 indicates the transmission range switches B and C are closed, connecting these circuits to ground. Park indicates the transmission range A switch is closed, connecting the circuit to ground. Reverse indicates the transmission range switches A, B, and P are closed, connecting these circuits to ground. Neutral indicates the transmission range switches B and P are closed, connecting these circuits to ground.

Injector PWM: Indicates the commanded pulse width modulation of the fuel injectors. The scan tool displays milliseconds.

Knock Retard: The scan tool range is 0-25.5 degrees. Indicates the amount of spark the PCM is removing from the IC spark advance in response to the signal from the knock sensors (KS). The traction control system desired torque signal from the electronic brake and traction control module (EBTCM) may cause knock retard to display a value more than 0 degrees if traction control is active.

Long Term FT: The scan tool range is -23 to +16 percent. Long term FT is derived from the short term FT value and represents a long-term correction of fuel delivery. A value of 0 percent indicates that fuel delivery requires no compensation to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0 percent indicates that the fuel system is rich and fuel delivery is being reduced, decreased injector pulse width. A positive value significantly more than 0 percent indicates that a lean condition exists and the PCM is compensating by adding fuel, increased injector pulse width. Because long term fuel trim tends to follow short term FT. A value in the negative range due to canister purge at idle should not be considered unusual. The PCMs maximum authority to control long term FT allows a range between -23 to +16 percent. Fuel trim values at or near maximum authority may indicate an excessively rich or lean system.

Loop Status:  The scan tool displays OPEN or CLOSED. Closed Loop indicates that the PCM is controlling fuel delivery according to oxygen sensor voltage. In Open Loop, the PCM ignores the oxygen sensor voltage and bases the amount of fuel to be delivered on throttle position (TP) sensor, engine coolant, and MAF sensor inputs only.

MAF Sensor: The scan tool range is 0.0-512 gm/s. Mass air flow (MAF) is the MAF input frequency converted to grams of air per second. This indicates the amount of air entering the engine.

MAF Sensor: The scan tool range is 0-32,000 Hz. The mass air flow sensor input signal to the PCM is a frequency which varies from around 3,000 Hz at idle to above 7,000 Hz at wide open throttle (WOT). The PCM converts this frequency signal to grams per second to be displayed on the scan tool as MAF.

MAP Sensor: The scan tool range is 10-105 kPa/0.00-4.97 volts. The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure from engine load, EGR flow, and speed changes. As intake manifold pressure increases, intake vacuum decreases resulting in a higher MAP sensor voltage and kPa reading. The MAP sensor signal is used in order to monitor the intake manifold pressure changes during the EGR flow test, to update the BARO reading, and as an enabling factor for many of the diagnostics.

MIL Circuit Status: Indicates the diagnostic state of the output driver for the MIL circuit. The scan tool displays Fault, OK or Invalid State.

MIL Command: The scan tool displays ON or OFF. Indicates the PCM commanded state of the malfunction indicator lamp (MIL).

Misfire Current Cyl. 1-6: The scan tool range is 0-198 counts. The misfire current counters indicate the number of cylinder firing events detected as possible misfires on each cylinder during the last 200 crankshaft revolutions. The number that the counters display are twice the actual number of misfire events detected. The counters may normally display some activity, but the activity should be very low and nearly equal for all the cylinders.

Misfire History Cyl. 1-6: The scan tool range is 0-65535 counts. The misfire history counters indicate the total level of misfire that has been detected on each cylinder. The number that the counters display are twice the actual number of misfire events detected. The misfire history counters will not update or show any activity until a misfire DTC P0300 has become active. The misfire history counters will be updated every time a 200 crankshaft revolution misfire test failure is detected.

Number of DTC(s): The scan tool displays a number. This parameter displays the quantity of active DTCs.

PCM / VCM in VTD Fail Enable: The scan tool displays ACTIVE or INACTIVE. If applicable, the theft deterrent fuel enable is an input from the vehicle theft deterrent (VTD) system that signals the PCM to enable the injectors and the crank relay if the proper signal is received. The scan tool will normally display INACTIVE. If the vehicle theft deterrent system does not send the correct theft deterrent fuel enable signal to the PCM, the display will switch to ACTIVE and the fuel system and starter control may be disabled. Refer to vehicle theft deterrent diagnosis for further information.

Power Enrichment: The scan tool displays ACTIVE or INACTIVE. ACTIVE displayed indicates that the PCM has detected conditions appropriate to operate in power enrichment mode. The PCM will command power enrichment mode when a large increase in throttle position and load is detected. While in power enrichment, the PCM will increase the amount of fuel delivered by entering Open Loop and increasing the injector pulse width. This is done in order to prevent a possible sag or hesitation from occurring during acceleration.

Short Term Fuel Trim:  The scan tool range is -11 to +20 percent. Short term FT represents a short-term correction to fuel delivery by the PCM in response to the amount of time the fuel control oxygen sensor voltage spends above or below the 450 mV threshold. If the oxygen sensor voltage has mainly remained less than 450 mV, indicating a lean air/fuel mixture, short term FT will increase into the positive range above 0 percent and the PCM will add fuel. If the oxygen sensor voltage stays mainly above the threshold, short term fuel trim will decrease below 0 percent into the negative range while the PCM reduces fuel delivery to compensate for the indicated rich condition. Under certain conditions such as extended idle and high ambient temperatures, canister purge may cause short term FT to read in the negative range during normal operation. The PCM's maximum authority to control fuel trim allows a range between -11 and +20 percent. Fuel trim values at maximum authority may indicate an excessively rich or lean system.

Spark: The scan tool range is -64 to +64 degrees. displays the spark timing being commanded by the PCM on the IC circuit. A negative (-) value indicates degrees before top dead center (BTDC) or spark advance. A positive value indicates degrees after top dead center (ATDC) or spark retard. Because the ignition control module sets spark advance at a fixed value of 10 degrees BTDC while operating in Bypass mode, the displayed spark advance only reflects true spark timing when the PCM has commanded IC mode.

Starter Enable Relay Circuit Status: Indicates the diagnostic state of the output driver for the starter enable relay control circuit. The scan tool displays Fault, OK or Invalid State.

Starter Relay Command: The scan tool displays ON or OFF. A Disabled display indicates that the PCM has inhibited starter relay operation. The PCM will inhibit starter relay operation if the engine is running, a correct VTD password has not been received from the VTD module or if the starter is engaged for an extended period of time.

Start-Up ECT: The scan tool range is -40 to +151°C (-40 to +304°F). Indicates the engine coolant temperature at the time that the vehicle was started. Used by the HO2S diagnostic in order to determine if the last startup was a cold start.

Start-Up IAT: The scan tool range is -40 to +151°C (-40 to +304°F). Indicates the intake air temperature at the time that the vehicle was started. Used by the HO2S diagnostic in order to determine if the last startup was a cold start.

TCC Brake Pedal Switch: Indicates the state of the switch. The scan tool displays Applied or Released.

TCC PWM Solenoid Command: Indicates the commanded PWM signal to the solenoid. The scan tool displays Hz.

TCS Circuit History: The scan tool displays Fault or OK This parameter saves the state of the driver circuit for this device.

TCS Circuit Status: Indicates the diagnostic state of the output driver for the traction control system (TCS) circuit. The scan tool displays Fault, OK or Invalid State.

TFP Switch: The scan tool displays PARK/NEUTRAL, REVERSE, DRIVE 4, DRIVE 3, DRIVE 2, or LOW. The TFP switch represents the decoded status of the four inputs from the internal transaxle fluid pressure switch assembly. The combination of these inputs indicates the position of the transaxle manual valve.

TP Sensor: The scan tool range is 0-100 percent. TP angle is computed by the PCM from the TP sensor voltage. TP angle should display 0 percent at idle and 100 percent at wide open throttle.

TP Sensor: The scan tool range is 0-5 volts. The voltage being monitored by the PCM on the TP sensor signal circuit.

Traction Control Status (If Equipped):  The scan tool displays ACTIVE or INACTIVE. ACTIVE displayed indicates that the traction control system is taking action in order to reduce drive wheel slippage.

Torque Request Signal (If Equipped):  The scan tool range is 0-100 percent. Represents the PWM signal from the electronic brake and traction control module. The EBTCM reduces the traction control desired torque signal pulse width when a drive wheel slippage situation is detected. The PCM monitors the traction control desired torque signal and reduces drive wheel slippage as necessary by retarding spark timing, decreasing boost solenoid PWM, or increasing air/fuel ratio. The PCM can also turn OFF up to three fuel injectors if the traction control desired torque signal indicates a large enough amount of drive wheel slippage. A problem with the traction control desired torque signal should cause DTC P1571 to set.

Torque Delivered Signal (If Equipped): The scan tool range is 0-100 percent. Represents the PWM signal which indicates the percent of available torque the engine is delivering to the drive wheels. The EBTCM monitors the traction control torque signal in order to ensure that the PCM is responding properly to the traction control desired torque signal.

Vehicle Speed:  The scan tool range is 0-255 km/h (0-155 mph). The vehicle speed sensor signal is converted into km/h and mph for display.

VTD Auto. Learn Timer: The scan tool displays ACTIVE or INACTIVE. The auto learn timer is the indication if the vehicle theft deterrent (VTD) system is in the learn mode and has not timed out.

VTD Fuel Disable: The scan tool displays ACTIVE or INACTIVE. If applicable, the theft deterrent fuel enable is an input from the vehicle theft deterrent system that signals the PCM to enable the injectors and the crank relay if the proper signal is received. The scan tool will normally display INACTIVE. If the vehicle theft deterrent system does not send the correct theft deterrent fuel enable signal to the PCM, the display will switch to ACTIVE and the fuel system and starter control may be disabled. Refer to vehicle theft deterrent diagnosis for further information.

VTD Fuel Disable Until Ign. OFF: The scan tool displays YES or NO With the ignition ON and a VTD code present, the scan tool displays YES.